A beam line ion implanter generates an ion beam and directs it at a workpiece for treatment. The workpiece may be, for example, a semiconductor wafer or another object receiving ion treatment for material modification. The beam line ion implanter includes an ion source to generate the ion beam and beam line components to control and direct the ion beam toward the workpiece. The beam line components may include a mass analyzer and a scanner downstream of the mass analyzer. The scanner is configured to scan the ion beam back and forth is in a scanned plane at a scan frequency to produce a scanned ion beam having trajectories which diverge from a scan origin. The scanner may be an electrostatic scanner or a magnetic scanner. An angle corrector downstream of the scanner accepts the scanned ion beam with diverging trajectories and deflects the same in an effort to produce more parallel trajectories of the scanned ion beam. The scanned ion beam may be distributed across a front surface of the workpiece by driving the workpiece orthogonal to the scanned plane.
The ions of the scanned ion beam strike the workpiece at an angle of incidence. Controlling this angle of incidence and minimizing a local beam angle spread of the ion beam is becoming increasingly important for some applications. One such application is a channeling ion implant into a semiconductor wafer. The semiconductor wafer may be fabricated of silicon and the crystalline lattice of the silicon may be oriented to promote channeling. If the angle of incidence varies slightly from a desired angle, the amount of channeling may be adversely reduced. The reduction in channeling is typically exacerbated at higher ion beam energies. Controlling the angle of incidence and the parallelism of the ion beam also helps to improve uniformity of the dose into a semiconductor wafer or other workpiece.
A conventional beam line ion implanter having a mass analyzer, a mass resolving aperture downstream of the mass analyzer, and a scanner focuses the ion beam to a focal point at the mass resolving aperture. Therefore, the ion beam has expanded by the time it reaches a scan origin of the scanner downstream of the mass resolving aperture. One drawback with this conventional beam line ion implanter is that the local beam angle spread of the ion beam may be unacceptably high for angle sensitive applications. In one experiment, a high energy [3 mega electron-volts (MeV)] ion beam of boron ions had a local beam angle spread of 0.06°. That is, the maximum deviation about a local beam angle mean was 0.06°. Such a deviation may adversely impact the amount of channeling and hence the resulting depth that dopant ions are implanted into a semiconductor wafer. In addition, the resulting uniformity of dose may also be adversely impacted.
Accordingly, it would be desirable to provide a beam line ion implanter and method which overcomes the above-described inadequacies and shortcomings.